The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is moved by several turbojet engines each housed in a nacelle.
A nacelle generally has a tubular structure comprising an air inlet upstream of the turbojet engine, a middle section intended to surround a fan of the turbojet engine, a downstream section accommodating a thrust reverser device and intended to surround the combustion chamber of the turbojet engine, and is generally ended by an ejection nozzle whose outlet is located downstream of the turbojet engine.
This nacelle is intended to accommodate a bypass turbojet engine able to generate through the blades of the rotating fan a hot air flow (also called primary flow), coming from the combustion chamber of the turbojet engine, and a cold air flow (secondary flow) which circulates outside the turbojet engine through an annular channel, also called flow path, formed between a fairing of the turbojet engine and an inner wall of the nacelle. The two air flows are ejected from the turbojet through the back of the nacelle.
The thrust reverser device is, during the landing of the aircraft, intended to improve the braking capacity thereof by redirecting forwards at least one portion of the thrust generated by the turbojet engine.
In this phase, the thrust reverser device obstructs the flow path of the cold air flow and directs the latter towards the front of the nacelle, thereby generating a counter-thrust which is added to the braking of the wheels of the aircraft, the means implemented to perform this reorientation of the cold air flow vary depending on the type of thrust reverser.
The means implemented to achieve this reorientation of the cold air flow vary depending on the thrust reverser type. However, the structure of a thrust reverser generally comprises movable cowls displaceable between, on the one hand, a deployed position in which they open within the nacelle a passage intended to the diverted flow, and on the other hand, a retracted position in which they close this passage. These cowls may fulfill a function of deflection or simply of activation of other diverting means.
Furthermore, besides its thrust reversal function, the thrust reverser cowl belongs to the downstream section of the nacelle and has a downstream portion forming the ejection nozzle aiming to channel the ejection of the air flows.
The optimal section of the ejection nozzle can be adapted depending on the different flight phases, namely the take-off, climb, cruise, descent and landing phases of the aircraft. The advantages already well known of such adaptive nozzles, also called variable section nozzles, are in particular the reduction of noise or the decrease of fuel consumption.
Among the variable section nozzles according to the prior art, the one described in the patent application published under the number FR 2 622 929, an embodiment of which is represented in FIG. 1, is in particular known. This application relates to a nacelle 1 for a turbojet engine, comprising an inner fixed structure 2 and an outer cowling 3 comprising an upstream section 5 and a downstream section 7 comprising a variable geometry nozzle 9.
A ring 10 of the downstream section of the outer cowling 3 is slidably mounted axially so as to create an opening 11 in the outer cowling 3. This opening 11 allows a portion of the air flow 13 circulating in the annular channel 15 to be ejected, which leads to enlarge the section of the nozzle formed by the cowl.
Although this type of nacelle allows effectively varying the section of the nozzle, it has some drawbacks.
The mechanical link between the upstream section 5 and the downstream section 7 of the outer cowling 3 constitutes a mechanical weakening of the nacelle.
Besides weakening the thrust reverser cowl, this mechanical link may also generate vibrations of the annular downstream section of the cowl during the operation of the engine.
It is also known from the prior art, the variable geometry nozzle 9 described in the patent application published under the number FR 2 946 696, represented in FIG. 2, in which the variation of the output section is made through doors 17 movably mounted in rotation between a position according to which they close an opening 19 of the outer cowling 3 and a position according to which they release said opening so as to eject a portion of the secondary air flow 13 to the outside of the nacelle and, consequently, to increase or reduce the output section of the nacelle.
As represented, this variable geometry nozzle 9 comprises a continuous downstream end portion 21, downstream of the opening 19 and the doors 17, which allows substantially increasing the structural strength of the nacelle, and solving the drawbacks of the prior art.
However, for a significant opening of the door, that is to say for a pivoting of the door 17 important enough (position which is not represented) to allow the passage of a sufficient amount of secondary air flow coming from the annular channel 15, the air flow which passes through the opening of the outer cowling and which escapes from the nacelle diverges, and is directed in a direction quasi-transverse to the longitudinal axis of the nacelle.
Such divergence of the air flow greatly affects the aerodynamic profile of the nacelle, and deteriorates the thrust performances of the propulsion assembly.
Furthermore, the doors of this nozzle have a relatively large and planar trailing edge 23, which results in a base-drag phenomenon, also affecting the aerodynamic profile of the nacelle and limiting the performances of the nozzle.